Variable antenna tuned to an odd number of quarter waves



Apnl 27, 1937. w. BUSCHBECK VARIABLE ANTENNA TUNED TO AN ODD NUMBER OFQUARTER WAVES Filed Dec. 16, 1935 2 Sheets-Sheet l m [MN/4 770? $5 x f(b/VOdCT'OA? (/voucrw? gm ATTORNEY.

Aprll 27, 1937- w. BUSCHBECK VARIABLE ANTENNA TUNED TO AN ODD NUMBER OFQUARTER WAVES Filed Dec. 16, 1935 2 Sheets-Sheet 2 INVENTOR.

K C E B H C S U B R F. N R F. W

Patented Apr. 27, 1937 UNITED STATES VARIABLE ANTENNA TUNED TO AN ODDNUMBER OF QUARTER WAVES Werner Buschbeck, Berlin, Germany, assignor toTelefunken Gesellschaft fur Drahtlose Telegraphic m. b. H., poration ofGermany Berlin, Germany, a cor- Application December 16, 1935, SerialNo. 54,588 In Germany January 17, 1935 8 Claims.

The present invention relates to antennae and is especially concernedwith avariable tuned vertical aerial having a grounded base directlyconnected with a concentric (coaxial) feeder or downlead.

It is well known that in the short wave field one may obtain relativelygreat wave-length ranges with an unvaried radiation diagram by usingcrank type antennae, wherein the aerial 1 is unreeled or paid out so asto result in a length of wire proportional to the wave length. Suchantennae present a terminal or base impedance independent of the wavelength.

It is particularly advantageous to make th length of the aerial suchthat the same will be tuned to \/4 or 3M4 or (2n-|-1) \/4, since inthese instances the antenna impedance at the terminal point is purelyohmic. By connection with a concentric or coaxial cable or downleadwhose characteristic impedance is equal to the terminal or baseresistance of the antenna, it is possible, as known from the prior art,to obtain a cable end free from reflection phenomena. Upon changes ofwave length, the aerial wire must be paid out or taken up. It has beensuggested previously to place the reeling device in a bulge of the innerconductor of the coaxial cable or download, as described in my UnitedStates Patent 2,036,456, granted April 7, 1936, the outer conductorbeing given a form so that the characteristc impedance of the line ispreserved in order that by the aerial wire to be taken up no additionalinductive or capacitive loads may be occasioned inadvertently at the endof the cable. This arrangement has proved quite satisfactory wheretransmitters of small or medium power are dealt with, while difiicultiesare encountered whenever large powers are concerned. The reel to beaccommodated in the interior of the cable, for constructional reasons,cannot be made of any desired size at all, and this places a limitationupon the maximum diameter which the antenna conductor may have. However,where relatively large powers are concerned, quite apart from thecurrent dissipated in heat, this means high field intensities on theconductor surface so that, under certain circumstances, the breakdownfield intensity in air may be exceeded. Where short waves are dealtwith, there are then observed the typical torches established by way ofsingle-pole capacity coupling with ground and which, within a shorttime, lead to the destruction of the antenna, not to speak of the factthat also the cable may be endangered for similar reasons. I

Stranded conductors when used for the outers,

even at the same diameter, are inferior to smooth tubes or wires becauseof their rough surface, so much more so as with repeated take-up andpayout some of the small wires of the strand are caused to break so thatthey may be conductive to corona.

Now, the present invention discloses methods of and means for overcomingthe foregoing disadvantages in a very simple manner. Upon tuning to,say, M4 the variable antenna length must be equal to A; (A max.-min.),if there is no capacitive end poise. Hence, if for instance, the waveband of a transmitter is to extend from 14 to 40 meters, it will be seenthat the length of the antenna must be capable of being varied a totalof 6.5 meters.

Figs. 1 and 2 disclose two different embodiments of the invention.

Now, according to the invention, the antenna consists of a stable smoothconductor A (Fig. 1) g of adequate diameter which telescopes inthe innerconductor D1 of a concentric vertically mounted energy feeder ordownload Di, Da having a characteristic impedance equal to the base endor terminal impedance of the antenna, rather than of a thin reelablestranded conductor. In order to avoid burying this conductor part verydeeply in the ground E, the antenna base point could also be placedabove the ground by the creation of a counterpoise Gg disposed at asuitable height (Fig. 1). In the embodiment here chosen, if the saidcounterpoise were mounted at an approximate height of 3 meters, thevertical part of the conductor would have to be buried under the groundonly about .3 of a meter, and this will :7

not be attended with serious difliculties in most instances. In orderthat bending of the antenna may be avoided, the antenna rod at itsbottom end could be loaded by a weight M so that merely tractilestresses are set up in case of changes in length. If the counterweight Mis properly chosen, a motor provided for insuring adjustments wouldmerely be called upon to cover the frictional losses; hence, themechanical traction could be chosen greater than is customary, and thiswould undoubtedly insure an improvement of the mechanical stability ofthe antenna.

In using greater wave-lengths or larger ranges or bands, the excavationwork may be simplified by building the vertical part of the downlead inthe way shown in Fig. 2. The conductor arrangement in Fig. 2 requiresthat the innermost part of a concentric double line D1 have the samecharacteristic impedance as the base or terminal point of the antenna.The inner conductor Du brought upwards by a further outer tube D2a whichis also concentric and grounded. What thus results for the return aretwo paralleled concentric (or coaxial) lines D1 and Dz=Dn against D13.and D21 against D25. which should be so dimensioned that their parallelresistance will also become equal to the resistance W at the antennabase. Hence, the whole downlead or coaxial cable part which must beburied con sists of a tube D23. being smooth on the outside, which, in away as known, for instance, from pinking wells, may be lowered into theground E. Connection between cable K and the inner conductor Ki and theouter conductor Ka is then eifected at the upper end of the energy lineD2 at some suitable and easily accessible point.

In order to avoid great lengths of vertical energy feeder leads wherethe wave length ranges or the wave lengths are still greater, it ispractical to build the antenna rod A of several telescoping tube pieces.The antenna rod A, which would be plunged to different depths into theinner conductor D1 of the downlead D in the presence of different wavelengths, would also allow of tele-indication of the effective antennalength either by mechanical or electrical means, for example, byarranging for the traction rope Z which connects the antenna rod A andthe antenna counterweight M with the mechanical balancing weight Mg topass over a pulley which in some convenient way drives an indicator orpointer device.

The invention, it will be understood, is not limited to the exactembodiments hereinbefore described .and illustrated, since variousmodifications can be made without departing from the spirit and scopethereon It is to be distinctly understood that the term odd multipleused in the specification and appended'claims is intended to mean anyodd multiple including one.

What is claimed is:

1. In combination, a vertical antenna tuned to have a length equal to anodd multiple of a quarter of the operating wave, a variable lengthsupport attached to the upper end of said antenna, a weight attached tothe lower end of said antenna, a concentric conductor system havinginner and outer tubular conductors located beneath said antenna, saidweight being free to move within said inner conductor as said antenna isvaried in length from said upper end, said inner conductor being inelectrical contact with said antenna.

2. In combination, a vertical antenna tuned to have a length equal to anodd multiple of a quarter Of the operating wave, a variable lengthsupport attached to the upper end of said antenna, a weight attached tothe lower end of said antenna, a hollow verticalconductor locateddirectly beneath said antenna, said weight being located and able tomove within said hollow conductor as said antenna is varied in length,and a counterpoise comprising a horizontal conducting element attachedsubstantially to the upper end of said hollow conductor.

3. In combination, a variable length antenna which is vertical for atleast the lower portion of its length, a weight attached to the lowerend of said antenna, a hollow vertical conductor located directlybeneath said antenna, said weight being located and able to move withinsaid hollow conductor as said antenna is varied in length, and acounterpoise comprising a horizontal conducting element attachedsubstantially to the upper end of said hollow conductor.

4. In combination, a variable length antenna adapted to be tuned to anodd multiple of a quarter of the operating wave and being vertical forat least the lower portion of its length, a weight attached to the lowerend of said antenna, a hollow vertical conductor located directlybeneath said antenna, said weight being located and able to move withinsaid hollow conductor as said antenna is varied in length, said lowerportion of said antenna above said weight being in electrical contactwith said hollow conductor.

5. In combination, a vertical antenna tuned to have a length equal to anodd multiple of quarter of the operating wave, a variable length supportattached to the-upper end of said antenna,

a weight attached to the lower end of saidantenna, a concentricconductor system having inner and outer'tubular conductors locatedbeneath said antenna, said weight being. free to move within said innerconductor as said antenna is varied in length from said upper end, saidinner conductor being in electrical contact with said antenna, saidconcentric conductor system having only a portion thereof extendingabove ground, the total length of said antenna outside and within saidconcentric conductors being capable of being varied a distancediiference between the largest and smallest wavelengths to which theantenna is adapted to be tuned, and a concentric energy feeder linecoupled above ground to said concentric conductor system.

.6. In combination, a vertical antenna tuned to have a length equal toan odd'multiple of a quarter of the operating wave, a variable lengthsupport attached to the upper end of said antenna, a weight attached tothe lower end of said.

antenna, a concentric conductor system having inner and outer tubularconductors located beneath said antenna, said weight being free to movewithin said inner conductor as said antenna is varied in length fromsaid upper end, said inner conductor being in electrical contact withsaid antenna, and a counterpoise connected to said outer conductor.

'7. An antenna system in accordance with claim 5, including acounterpoise connected to the upper part of said outer tubularconductor.

8. In combination, a vertical antenna tuned to have a length equal to anodd multiple of a quarter of the operating wave, a variable lengthsupport attached to the upper end of said antenna, a weight attached tothe lower end of said antenna, a concentric conductor system havinginner and outer tubular conductors located beneath said antenna, saidinner and outer tubular conductors being folded back for a substantialportion of said concentric conductor system, said weight being free tomove withinj'said inner conductor as said antenna is varied in lengthfrom said upper end, said inner conductor being in electrical contactwith said antenna, and a feeder coupled to said folded back portion.

WERNER BUSCHBECK.

